Nonaqueous polymerization of fluoromonomers

ABSTRACT

The present invention provides a process for making fluorinated polymers and copolymers having stable end groups. The process includes (1) contacting a fluoromonomer, an initiator capable of producing stable end groups on the polymer chain, and a polymerization medium comprising carbon dioxide, and (2) polymerizing the fluoromonomer. The polymerization medium preferably comprises liquid or supercritical carbon dioxide. Advantageously, the process may also include the step of separating the fluoropolymer from the polymerization medium. 
     The present invention also provides polymerization reaction mixtures useful in the processes of the present invention.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/402,202 filed 10 Mar. 1995, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a nonaqueous polymerization process formaking fluorinated polymers, including copolymers thereof, in a mediumcomprising carbon dioxide.

BACKGROUND OF THE INVENTION

Two essential techniques have been employed for the polymerization offluoromonomers. The most inexpensive and commercially employed techniqueinvolves the use of a water-soluble polymerization initiator, and isknown as an "aqueous polymerization system." The disadvantage of aqueouspolymerization systems is that the resulting fluoropolymers haveunstable end groups which are undesirable for many applications. Some ofthese end groups, such as ionic end groups, carboxylic acid end groupsand acid fluoride end groups are hydrolytically unstable or decomposeunder specific processing techniques, resulting in bubbles ordiscolorations. These undesirable end groups can be avoided through theuse of nonaqueous polymerization systems.

One needs to be careful when choosing a non aqueous medium forfluoromonomer polymerization systems so that the medium does not lead toexcessive chain transfer reactions. This is because upon treatment of afluoromonomer, such as tetrafluoroethylene, with a free radicalinitiator, the result is a propagating radical chain end that is highlyelectrophilic. Such highly electrophilic fluorinated radicals are proneto extensive chain transfer to conventional solvents. In addition, innonaqueous polymerization systems, the initiator must be relativelysoluble in the nonaqueous medium employed and the initiator must bechosen to give polymers that have stable end groups which do notdecompose during processing. One nonaqueous polymerization systeminvolves the use of fluorinated initiators and chlorofluorocarbonpolymerization media, such as that described in U.S. Pat. No. 3,642,742to Carlson. However, in light of the identification ofchlorofluorocarbons as one of the primary factors in atmospheric ozonedepletion, extensive effort has been directed toward discoveringalternative polymerization media systems for fluoropolymerizations.

U.S. Pat. No. 3,642,742 to Carlson discloses one alternativepolymerization system involving the use of a fluorinated initiator, ahydrogen containing chain transfer agent, and a fluorocarbon medium.U.S. Pat. No. 5,182,342 to Feiring et al. discloses the use ofhydrofluorocarbons as yet another alternative to chlorofluorocarbonsystems. Perfluorocarbon and hydrofluorocarbon media are disadvantageousin that they are expensive. Other fluoropolymerization media which havebeen explored include perfluoroalkyl sulfide fluids, as described in U.SPat. No. 5,286,822 to Krespam et al., and perfluorinated cyclic amines,as described in U.S. Pat. No. 5,310,836 to Treat. However, these mediaare also expensive.

As an alternative polymerization media, researchers have recently begunexploring the use of carbon dioxide as a polymerization medium. Forexample, U.S. Pat. No. 3,522,228 to Fukui et al. discloses thepolymerization of vinyl monomers using peroxide polymerizationinitiators in liquid carbon dioxide at temperatures from -78° C. to 100°C. Fukui provides no example of a fluoromonomer polymerization in acarbon dioxide solvent, and indeed the methods disclosed therein havefailed to achieve commercial utility for the preparation offluoropolymers. In addition, Fukui fails to recognize the important roleof stable end groups in fluoropolymers. U.S. Pat. No. 5,328,972 to Dadaet al. discloses a process for the production of low molecular weightpolymers of C₃ -C₄ monoethyleneically unsaturated monocarboxylic acidsin supercritical carbon dioxide at temperatures of at least 200° C. andpressures above 3,500 psi. U.S. Pat. No. 5,345,013 to Van Bramer et al.proposes mixtures of tetrafluoroethylene monomer and carbon dioxide forsafe handling, but does not discuss fluoropolymerization methods.

PCT Publication No. WO 93/20116 to University of North Carolina atChapel Hill discloses processes for making fluoropolymers comprisingsolubilizing a fluoromonomer in a solvent comprising carbon dioxide. PCTPublication No. 93 WO/20116 is not concerned with the problem ofpolymerizing fluoromonomers to provide polymers having stable endgroups.

Accordingly, there remains a need in the art for a method of makingfluoropolymers having stable end groups which avoids the use ofpolymerization media which are detrimental to the environment, such aschlorofluorocarbons. There is also a need in the art forfluoropolymerization processes capable of commercialization, whichproduce fluoropolymers having stable end groups, and which utilizenonhazardous, relatively inexpensive polymerization media which arerelatively easily separable from the fluoropolymer produced.

SUMMARY OF THE INVENTION

As a first aspect, the present invention provides a process for makingfluorinated polymers having stable end groups. The process includes (1)contacting a fluoromonomer, an initiator capable of producing stable endgroups, and a polymerization medium comprising carbon dioxide, and (2)polymerizing the fluoromonomer. The polymerization medium preferablycomprises liquid or supercritical carbon dioxide, and may include othercosolvents as described in detail hereinbelow. The fluoromonomers usefulin the methods of the present invention include monomers having at leastone fluorine bound to a vinyl carbon and monomers having at least oneperfluoroalkyl group bound to a vinyl carbon. The initiators useful inthe method of the present invention are typically halogenated freeradical initiators, and are soluble in the polymerization medium.Advantageously, the process may also include the step of separating thefluoropolymer from the polymerization medium.

As a second aspect, the present invention provides a process for makinga fluorinated copolymer having stable end groups. The process includes(1) contacting a fluoromonomer, one or more comonomers capable ofcopolymerizing with the fluoromonomer, and an initiator capable ofproducing stable end groups, in a polymerization medium comprisingcarbon dioxide, and (2) copolymerizing the fluoromonomer and thecomonomer in the polymerization medium.

As a third aspect, the present invention provides a polymerizationreaction mixture useful for carrying out the polymerization of afluoromonomer to produce a fluorinated polymer having stable end groups,said reaction mixture include: (a) a fluoromonomer; (b) an initiatorcapable of producing stable end groups on said polymer; and (c) apolymerization medium comprising liquid or supercritical carbon dioxide.

As a fourth aspect, the present invention provides a polymerizationreaction mixture produced by the polymerization of a fluoromonomerincluding: (a) a fluorinated polymer having stable end groups; and (b) apolymerization medium comprising liquid or supercritical carbon dioxide.

The foregoing and other aspects of the present invention are explainedin detail in the specification set forth below.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "supercritical" has its conventional meaning inthe art. A supercritical fluid (SCF) is a substance above its criticaltemperature and critical pressure (or "critical point"). Compressing agas normally causes a phase separation and the appearance of a separateliquid phase. However, if the fluid is in a supercritical state,compression will only result in density increases; no liquid phase willbe formed. The use of supercritical fluids for carrying outpolymerization processes has received relatively little attention. Theterm "fluoropolymer," as used herein, has its conventional meaning inthe art. See generally Fluoropolymers (L. Wall, Ed. 1972)(Wiley-Interscience Division of John Wiley & Sons); See alsoFluorine-Containing Polymers, 7 Encyclopedia of Polymer Science andEngineering 256 (H. Mark et al. Eds., 2d Ed. 1985). Likewise, the term"fluoromonomer" refers to fluorinated precursor monomers employed in thesynthesis of fluoropolymers. The phrase "stable end group(s)" as usedherein refers to polymer chain end groups which essentially do notdecompose when the polymer is heated to its melt processing temperature.Such processing temperatures are generally known in the art, such asthose described in Banks et al. Organofluorine Chemistry: Principles andCommercial Applications (1994). Specific examples of stable end groupsinclude but are not limited to perfluoroalkyl end groups,perfluoroalkoxy end groups, perchloroalkyl end groups, and the like.Typically, a polymer having stable end groups is a polymer which hasfewer unstable end groups than would be observed in the same polymer,having substantially the same molecular weight, prepared according toaqueous polymerization techniques. More specifically, a polymer havingstable end groups is typically a polymer which has less than 400unstable end groups which can be acid fluoride or carboxylic acid endgroups, per million carbon atoms. In particular embodiments, a polymerhaving stable end groups is a polymer which has 300 or less, 200 orless, or 100 or less, unstable end groups as defined above per millioncarbon atoms.

The fluoromonomers useful in the processes of the present inventioninclude any suitable fluoromonomers known to those skilled in the art.The fluoromonomers may be in a gaseous or liquid state. Generally, thefluoromonomers useful in the processes of the present invention arehomopolymerizable or copolymerizable by a free radical mechanism.Preferred fluoromonomers will contain at least one fluorine atom,perfluoroalkyl group, or perfluoroalkoxy group directly attached to thevinyl group that undergoes polymerization. Examples of suitablefluoromonomers include, but are not limited to, perfluoroolefins,particularly tetrafluoroethylene; perfluoro(alkyl vinyl ethers) withperfluoroalkyl groups containing 1 to 6 carbon atoms and thosecontaining functional groups such as CF₂ ═CFOCF₂ CF(CF₃)OCF₂ CF₂ SO₂ Fand CF₂ ═CFOCF₂ CF(CF₃)OCF₂ CF₂ CO₂ CH₃ ; hexafluoropropylene;perfluoro(2,2-dimethyldioxole); fluorodienes, such as CF₂ ═CFO(CF₂)_(n)CF═CF₂ and CF₂ ═CFOCH₂ (CF₂)_(n) CF═CF₂ ; and partially fluorinatedmonomers, particularly vinyl fluoride, vinylidene fluoride,chlorotrifluoroethylene, hexafluoroisobutylene, and perfluoroalkylethylenes with perfluoroalkyl groups containing 1 to 6 carbon atoms.Copolymers of fluorinated monomers with nonfluorinated monomers,particularly ethylene, propylene, vinylacetate, alkylvinyl ethers,acrylates, methacrylates, and styrenics may also be included. Copolymersof fluorinated monomers with monomers having a functional group suitablefor crosslinking, such as bromotrifluoroethylene andbromodifluoroethylene may also be included. Preferred fluoromonomersinclude tetrafluoroethylene, hexafluoropropylene, perfluoromethylvinylether, perfluoroethylvinyl ether, perfluoropropylvinyl ether, vinylfluoride, vinylidene fluoride, chlorotrifluoroethylene, andperfluoro(2,2-dimethyl dioxole).

The fluoropolymers produced according to the processes of the presentinvention include homopolymers of any of the foregoing fluoromonomers,or in the embodiment wherein one or more comonomers are employed incombination with the fluoromonomer, the resulting fluoropolymers may becopolymers. Examples of homopolymers which may be produced according tothe methods of the present invention include but are not limited topolytetrafluoroethylene, polyvinylfluoride, polyvinylidine fluoride,polychlorotrifluoroethylene, polyhexafluoroisobutylene, and the like.

The comonomers useful in the methods of the present invention may befluoromonomers (as indicated above), or they may be non-fluorinatedmonomers which are capable of copolymerizing with the fluoromonomers ofthe present invention. Suitable non-fluorinated comonomers include thosedescribed above.

Copolymers which may be produced according to the processes of thepresent invention include but are not limited totetrafluoroethylene/hexafluoropropylene,

tetrafluoroethylene/hexafluoropropylene/vinylidine fluoride,

hexafluoropropylene/vinylidine fluoride,

perfluoro(methyl vinyl ether)/vinylidine fluoride,

perfluoro(methyl vinyl ether)/vinylidinefluoride/tetrafluoroethylene,

chlorotrifluoroethylene/vinylidine fluoride,

chlorotrifluoroethylene/ethylene,

chlorotrifluoroethylene/tetrafluoroethylene/ethylene,

tetrafluoroethylene/perfluoro(propyl vinyl ether),

tetrafluoroethylene/perfluoro(methyl vinyl ether),

tetrafluoroethylene/perfluoro(2,2-dimethyl-1,3-dioxole),

tetrafluoroethylene/ethylene,

tetrafluoroethylene/propylene,

tetrafluoroethylene/CF₂ ═CFOCF₂ CF(CF₃)OCF₂ CF₂ SO₂ F,

tetrafluoroethylene/CF₂ ═CFOCF₂ CF₂ SO₂ F,

tetrafluoroethylene/hexafluoropropylene/perfluoro(propyl vinyl ether),and

tetrafluoroethylene/CF₂ ═CFO(CF₂)_(n) CF═CF₂.

Preferred copolymers which may be produced according to processes of thepresent invention include perfluorinated copolymers such as

tetrafluoroethylene/perfluoro(propyl vinyl ether),

tetrafluoroethylene/hexafluoropropylene,

tetrafluoroethylene/perfluoro(2,2-dimethyl-1,3-dioxide),

tetrafluoroethylene/perfluoro(methyl vinyl ether),

tetrafluoroethylene/CF₂ ═CFOCF₂ CF₂ SO₂ F, and

tetrafluoroethylene/CF₂ ═CFOCF₂ (CF₃)OCF₂ CF₂ SO₂ F.

In the processes of the present invention, the fluoromonomers arepolymerized in the presence of a polymerization initiator. The initiatoris capable of providing a stable end group on the polymer chain.Generally, the initiator becomes part of the polymer chain.Consequently, upon the termination of polymerization, the initiatorprovides the end group for the polymer chain. Examples of suitableinitiators which are capable of providing a stable end group include butare not limited to halogenated initiators. Suitable halogenatedinitiators include, for example, chlorinated and fluorinated initiators,which are capable of decomposing into free radical species. Initiatorswhich are soluble in the polymerization medium are preferred. Forexample, suitable polymerization initiators include chlorocarbon basedand fluorocarbon based acyl peroxides such as trichloroacetyl peroxide,bis(perfluoro-2-propoxy propionyl) peroxide, CF₃ CF₂ CF₂ OCF(CF₃)COO!₂,perfluoropropionyl peroxides, (CF₃ CF₂ CF₂ COO)₂, (CF₃ CF₂ COO)₂, {(CF₃CF₂ CF₂) CF(CF₃)CF₂ O!_(n) CF(CF₃)COO}₂, ClCF₂ (CF₂)_(n) COO!₂, wheren=0-8; perfluoroalkyl azo compounds such as perfluoroazoisopropane,(CF₃)₂ CFN═!₂ ; R₄ N═NR₄, where R₄ is a linear or branchedperfluorocarbon group having 1-8 carbons; stable or hinderedperfluoroalkane radicals such as hexafluoropropylene trimer radical,(CF₃)₂ CF!₂ (CF₂ CF₂)C. radical and perfluoroalkanes. Preferably, theinitiator is a fluorinated initiator, and more preferably the initiatoris selected from the group consisting of bis(perfluoro-2-propoxypropionyl) peroxide, perfluoropropionyl peroxide,perfluoroazoisopropane, and hexafluoropropylene trimer radical.

The stable end group which is provided by the polymerization initiatoris a function of the particular initiator employed. Typically, thestable end group is a perfluoroalkyl, perfluoroalkoxy, or perchloroalkylend group inasmuch as the initiators typically contain such groups.These end groups are thermally and hydrolytically stable duringconventional fluoropolymer processing conditions, and do not decomposeto other species.

The processes of the invention are carried out in a polymerizationmedium comprising carbon dioxide. The carbon dioxide is typically in aliquid or supercritical state. Preferably the polymerization medium issupercritical carbon dioxide. In a supercritical polymerization medium,only a single fluid phase is present; as a result, the effectiveconcentration of a gaseous monomer, such as tetrafluoroethylene, isdirectly a function of the amount charged and is not dependent upon thesolubility of the gaseous monomer in a liquid polymerization medium.This presents an advantage in terms of copolymer composition control. Inaddition, supercritical carbon dioxide is a highly tunablepolymerization medium and allows the manipulation of solvent strengthand density through simple changes in temperature and pressure, which inturn allows an additional measure of control over reaction parameters.Supercritical carbon dioxide also offers high mass transport rates andlow fluid viscosity.

The polymerization medium may also include one or more cosolvents.Illustrative cosolvents include but are not limited to,perfluorocarbons, hydrofluorocarbons, perfluoroalkyl sulfides, and like.It may be desirable for the cosolvent to be capable of solubilizing theinitiator such that the initiator may be provided to the reaction in thesolubilized form.

The initiator may be added in neat form, as a solution in carbondioxide, or it may conveniently be added as a solution in a cosolvent.Typically, the initiator is used in an amount conventionally employedfor polymerization. The amount of initiator employed depends on severalfactors, including the specific monomers and comonomers to bepolymerized, the reactivity of the monomers or comonomers, the reactionconditions, and the particular initiator chosen. For example, theinitiator may be used in an amount of about 10⁻⁶ to 10, preferably about10⁻⁵ to 2, parts by weight per 100 parts by weight monomer.

The polymerization reaction mixture may include other additives andreactants known to those skilled in the art for controlling the physicalor chemical properties of the resulting polymer. For example, in onepreferred embodiment, the polymerization reaction mixture includes achain transfer agent for regulating the molecular weight of theresulting polymer. Suitable chain transfer agents will be readily knownto those skilled in the art and include, for example, hydrocarbons suchas ethane and methyl cyclohexane; alcohols, such as methanol;mercaptans, such as ethyl and butyl mercaptan; sulfides, such as butylsulfide; and halogenated hydrocarbons such as alkyl iodides,perfluoroalkyl iodides, alkyl bromides, perfluoroalkyl bromides, carbontetrachloride, and chloroform. As will be appreciated by those skilledin the art, when chain transfer agents are employed a significant numberof end groups are derived from the chain transfer agent. As a resultchain transfer agents should be selected so as to avoid the formation ofunstable end groups. Preferred chain transfer agents include ethane andchloroform.

It may be desirable to also include compounds which accelerate thedecomposition of the initiator. Such compounds typically permit thepolymerization reaction to take place a lower pressures than wouldotherwise be required, thus permitting the methods of the presentinvention to be practiced in conventional fluoropolymerization reactors.Suitable compounds which accelerate decomposition are known to thoseskilled in the art and include but are not limited to, redox systems,sulfur dioxide, ultraviolet light, and others.

The polymerization reaction may be carried out at a temperature of about-50° C. up to about 200° C., and is typically carried out at atemperature of between about -20° C. and about 150° C. The reaction maybe carried out at a pressure ranging from about 15 psi to about 45,000psi, and is typically carried out at a pressure of between about 500 psiand about 10,000 psi.

The polymerization can be carried out batchwise or continuously withthorough mixing of the reactants in any appropriately designed highpressure reaction vessel. To remove the heat evolved during thepolymerization, advantageously the pressure apparatus includes a coolingsystem. Additional features of the pressure apparatus used in accordancewith the invention include heating means such as an electric heatingfurnace to heat the reaction mixture to the desired temperature andmixing means, i.e., stirrers such as paddle stirrers, impeller stirrers,or multistage impulse countercurrent agitators, blades, and the like.

The polymerization can be carried out, for example, by feeding a mixtureof monomer and carbon dioxide into a pressure apparatus containing theinitiator. The reaction vessel is closed and the reaction mixturebrought to the polymerization temperature and pressure. Alternatively,only a part of the reaction mixture may be introduced into an autoclaveand heated to the polymerization temperature and pressure, withadditional reaction mixture being pumped in at a rate corresponding tothe rate of polymerization. In another possible procedure, some of themonomers are initially taken into the autoclave in the total amount ofcarbon dioxide and the monomers or comonomers are pumped into theautoclave together with the initiator at the rate at which thepolymerization proceeds. Continuous or semibatch modes of addition maybe useful to control polymer composition and composition distribution.These modes are particularly useful in copolymerization of two monomerswith dramatically different reactivities such as tetrafluoroethylene andhexafluoropropylene.

When the polymerization is complete the polymer may be separated fromthe reaction mixture. Any suitable means of separating the polymer fromthe reaction mixture may be employed. Typically, according to theprocess of the present invention, the polymer is separated from thereaction mixture by venting the polymerization medium to the atmosphere.Thereafter the polymer may be collected by physical isolation.

It may be desirable, for some applications to wash the resulting polymerprior to further processing. The polymer is preferably washed in a washfluid comprising carbon dioxide prior to or after venting thepolymerization medium to the atmosphere and collecting the polymer.Typically, the wash fluid comprises carbon dioxide, or a mixture ofcarbon dioxide with methanol, amines such as ammonia, or fluorine gas.The methanol, amines, or fluorine gas may be introduced into the reactorcontaining the polymerization medium by suitable means known to thoseskilled in the art.

The fluoropolymers produced according to the processes of the presentinvention contain stable end groups. Preferably, the fluoropolymerscontain perfluoroalkyl, perfluoroalkoxy, or perchloroalkyl end groups.These fluoropolymers are useful in areas where conventionalfluoropolymers are employed, and particularly as wire coatings, gaskets,seals, hoses, vessel linings, elastomers, molded resins, protectivecoatings, and the like.

The following examples are provided to illustrate the present invention,and should not be construed as limiting thereof. In these examples,"psi" means pounds per square inch; "g" means grams; "mg" meansmilligrams; "mL" means milliliters; "min." means minutes; "FTIR" meansfourier transform infrared; "IR" means infrared; and "° C." meansdegrees celsius. Molecular weight is estimated using the methoddescribed in T. Suwa, et al., J. Applied Polymer Sci. 17:3253 (1973).

EXAMPLE 1

Tetrafluoroethylene homopolymer

A 25 ml high pressure reactor is cooled to well below 0° C. in a dryice/acetone bath under argon. A 0.018M solution of HFPO dimer peroxideinitiation of 1,1,2-trichlorotrifluoroethane (0.050 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed. A 50/50wt./wt. % mixture (9.7 g) of tetrafluoroethylene (4.8 g) and carbondioxide (4.8 g) is condensed into the reactor at a temperature of below-20° C., and CO₂ (10 g) is added via high pressure syringe pump. Thereactor is slowly heated to 35° C. and held for 3 hours. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened, and the productcollected. The product is washed twice with1,1,2-trichlorotrifluoroethane/methanol (1:1) and dried under vacuum atelevated temperature. The reaction yields 1.57 g of a white polymer (32%yield). Thermogravimetric shows a 5% weight loss at 533.2° C.Differential scanning calorimetry shows a virgin melting point of 328.5°C., a second melt of 328.5° C., and a crystallization exotherm at 308.7°C. (second cooling) yielding a heat of crystallization of 50.6 J/gcorresponding to an estimated molecular weight of 55,000 g/mol.

EXAMPLE 2

Tetrafluoroethylene homopolymer

A 25 ml high pressure reactor is cooled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.010 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed. A 50/50wt./wt. % mixture (12.9 g) of tetrafluoroethylene (6.4 g) and carbondioxide (6.4 g) is condensed into the reactor at a temperature of below-20° C., and 10 g CO₂ (10 g) is added via high pressure syringe pump.The reactor is slowly heated to 35° C. and held for 4 hours. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened, and the product iscollected. The product is washed twice. After washing twice with a 50/50mixture of 1,1,2-trichlorotrifluoroethane/methanol, the product is driedunder vacuum at elevated temperature. The reaction yields 6.47 grams ofwhite polymer (100% yield). Thermogravimetric analysis shows a 5% weightloss at 537.2° C. Differential scanning calorimetry shows a virginmelting point of 334.9° C., a second melt of 328.5° C., acrystallization exotherm at 309.2° C. (second cooling), yielding a heatof crystallization of 41.2 J/g corresponding to an estimated molecularweight of 160,000 g/mol.

EXAMPLE 3

PPVE/TFE Copolymer

A 25 ml high pressure reactor is cooled to well below 0° C. in a dryice/acetone bath under argon. A 0.018M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.10 ml) perfluoro(propylvinyl ether) (0.80 ml, 1.2 g), which has been sparged with argon areadded while maintaining a positive argon purge, and the reactor issealed. A 50/50 wt./wt. % mixture (10.5 g) of tetrafluoroethylene (5.2g) and carbon dioxide (5.2 g) is condensed into the reactor at atemperature of below -20° C., and CO₂ (10 g) were added via highpressure syringe pump. The reactor is slowly heated to 35.0° C., andheld for 4 hours. The reactor window gradually becomes cloudy over thefirst thirty minutes after which time the window appears white and nofurther change can be observed. After the reaction is complete thecarbon dioxide and excess monomer are vented slowly to the atmosphere,the reactor is opened and the product collected. The product is washedtwice with a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanoland dried under vacuum at elevated temperature. The reaction yields 5.32g of white polymer (100% yield based on TFE). Thermogravimetric analysisshows a 5% weight loss at 535.0° C. Differential scanning calorimetryshows a virgin melting point of 330.5° C., a second melt of 328.5° C.,and a crystallization exotherm at 303.3° C. (second cooling). End groupanalysis by FTIR found no detectable acid fluoride or carboxylic acidend groups.

For copolymers incorporating fluorinated vinyl ether monomers, such asperfluoro(propyl vinyl ether), unstable acid fluoride end groups may beobserved when polymerization is carried out in conventionalpolymerization media such as 1,1,2-trichlorotrifluoroethane, even thoughthe initiators employed are capable of providing stable end groups. Theunstable acid fluoride end groups are believed to result from chaintransfer/rearrangement side reactions involving the fluorinated alkylvinyl ether. U.S. Pat. No. 4,743,658 to Imbalzano et al., the disclosureof which is hereby incorporated by reference in its entirety, discussescopolymers of perfluoro(propyl vinyl ether) and tetrafluoroethyleneprepared using a perfluorinated acid peroxide in a1,1,2-trichlorotrifluoroethane polymerization medium. The resultingImbalzano et al. copolymer exhibits 138 acid fluoride end groups permillion carbon atoms. In contrast, the combined acid fluoride andcarboxylic acid end groups for copolymerizations conducted in accordancewith the present invention in carbon dioxide were not greater than 11unstable groups per million carbon atoms. This result indicates that theinitiators employed in the present invention in combination with thecarbon dioxide polymerization medium advantageously reduce the number ofunstable end groups to a significant degree. It is believed that thecarbon dioxide polymerization medium of the present invention limits thefluoroalkyl vinyl ether rearrangement, thus producing fewer unstable endgroups. For the reaction run in carbon dioxide and methanol, as a chaintransfer agent, 80 methyl ester end groups were observed per millioncarbon atoms.

EXAMPLE 4

PPVE/TFE Copolymer

A 25 ml high pressure reactor is cooled to well below 0° C. in a dryice/acetone bath under argon. A 0.018M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.10 m) andperfluoro(propyl vinyl ether) (0.80 ml, 1.2 g) which has been spargedwith argon are added while maintaining a positive argon purge, and thereactor is sealed. A 50/50 wt./wt. % mixture (9.4 g) oftetrafluoroethylene (4.7 g) and carbon dioxide (4.7 g) is condensed intothe reactor at a temperature of below -20° C., and CO₂ (10 g) is addedvia high pressure syringe pump. The reactor is slowly heated to 35.0° C.and held for 3 hours at which time heating is discontinued. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 4.67 g of white polymer (99%yield based on TFE). Thermogravimetric analysis shows a 5% weight lossat 524.2° C. Differential scanning calorimetry shows a virgin meltingpoint of 321.5° C., and a crystallization exotherm at 291.3° C. (firstcooling). End group analysis by FTIR found no detectable acid fluorideor carboxylic acid end groups.

EXAMPLE 5

TFE/PPVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.10 ml) and 2.4 ml (3.7)perfluoro(propyl vinyl ether) (2.4 ml, 3.7 g) which has been spargedwith argon, are added while maintaining a positive argon purge, and thereactor is sealed. A 50/50 wt./wt. % mixture (11.0 g) oftetrafluoroethylene(5.5 g) and carbon dioxide (5.5 g) is condensed intothe reactor at a temperature of below -20° C., and CO₂ (10 g) is addedvia high pressure syringe pump. The reactor is slowly heated to 35° C.and held for 4 hours at which time heating is discontinued. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 5.58 g of white polymer (100%yield based on TFE). Thermogravimetric analysis shows a 5% weight lossat 494.0° C. Differential scanning calorimetry shows a virgin meltingpoint of 318.6° C. and a crystallization exotherm at 300.9° C. (firstcooling). End group analysis by FTIR found a combined total of threeacid fluoride and carboxylic acid end groups per 10⁶ carbon atoms.

EXAMPLE 6

TFE/PPVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.080 ml) andperfluoro(propyl vinyl ether) (2.4 ml, 3.7 g) which has been spargedwith argon, is added while maintaining a positive argon purge, and thereactor is sealed. A 50/50 wt./wt. % mixture (10.1 g) oftetrafluoroethylene (5.0 g) and carbon dioxide (5.0 g) is condensed intothe reactor at a temperature of below -20° C. and CO₂ (10 g) is addedvia high pressure syringe pump. The reactor is then slowly heated and atca. 22° C. an exothermic reaction brings the temperature to 50.9° C.After several minutes the temperature decreases to 35 and is maintainedfor 4 hours at which time heating is discontinued. The cell windowgradually becomes cloudy over the first few minutes after which time thewindow appears white and no further change can be observed. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened, and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 5.03 g of white polymer (100%yield based on TFE). Thermogravimetric analysis shows a 5% weight lossat 511.1° C. Differential scanning calorimetry shows a virgin meltingpoint of 312.7° C., and a crystallization exotherm at 294.0° C. (firstcooling). Analysis by FTIR observed 5.20 wt. % perfluoro(propylvinylether) incorporation and only 1.7 carboxylic acid and 2.5 carboxylicacid fluoride end groups per 10⁶ carbon atoms.

EXAMPLE 7

TFE/PPVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.08 ml) andperfluoro(propyl vinyl ether) (4.0 ml, 6.1 g) which has been spargedwith argon, are added while maintaining a positive argon purge, and thereactor is sealed. A 50/50 wt./wt. % mixture (11.2 g) oftetrafluoroethylene (5.6 g) and carbon dioxide (5.6 g) is condensed intothe reactor at a temperature of below -20° C. and CO₂ (10 g) is addedvia high pressure syringe pump. The reactor is slowly heated and at ca.25.0° C. an exothermic reaction brings the temperature to 52.0° C. Afterseveral minutes, the temperature decreases to 35° C. where it ismaintained for 4 hours, at which time heating is discontinued. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened, and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 5.67 g of white polymer (100%yield based on TFE). Thermogravimetric analysis shows a 5% weight lossat 511.4° C. Differential scanning calorimetry shows a virgin meltingpoint of 313.7° C., and a crystallization exotherm at 295.0° C. (firstcooling). Analysis by FTIR observed 5.77 wt. % perfluoro(propylvinylether) incorporation and only 2.7 carboxylic acid and less than 3carboxylic acid fluoride end groups per 10⁶ carbon atoms.

EXAMPLE 8

TFE/PPVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice bath under argon. A 0.24M solution ofbis(perfluoro-2-propoxypropionyl)peroxide in F-113 (0.05 ml) andperfluoro(propyl vinyl ether) (5.0 ml, 7.6 g) which had previously beensparged with argon, are added while maintaining a positive argon purgeand the reactor is sealed. A 50 wt./wt. % mixture (9.8 g) oftetrafluoroethylene (4.9 g) and carbon dioxide (4.9 g) is condensed intothe reactor at a temperature of below <20° C., and CO₂ (10 g) is addedvia high pressure syringe pump. The reactor is slowly heated to 35° C.and held for 3.5 hours at which time heating is discontinued. After thereaction is complete the carbon dioxide and excess monomer are ventedslowly to the atmosphere, the reactor is opened, and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane and dried under vacuum at elevatedtemperature. The reaction yields 5.05 g of product (100% yield based onTFE). Thermogravimetric shows a 5% weight loss at 512.1° C. Differentialscanning calorimetry shows a virgin melting point of 317.6° C., and acrystallization exotherm at 298.9° C. (first cooling).

EXAMPLE 9

TFE/HFP Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.024M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.050 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Hexafluoropropylene (19.3 g) and a 50/50 wt./wt. % mixture (3.4 g) oftetrafluoroethylene (1.7 g) and carbon dioxide (1.7 g) are condensedinto the cell at a temperature of below -20° C. The reactor is slowlyheated to 35.0° C. and held for 8 hours. After the reaction time iscomplete the carbon dioxide and excess monomer are vented slowly to theatmosphere, the reactor is opened, and the product collected. Theproduct is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane and dried under vacuum at elevatedtemperature. The reaction yields 0.052 g of white polymer (3.1% yield).Thermogravimetric analysis shows a 5% weight loss at 410.0° C.Differential scanning calorimetry shows a virgin melting point of 249.7°C., and a crystallization exotherm at 242.8° C. (first cooling).

EXAMPLE 10

TFE/HFP Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.18M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.050 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Hexafluoropropylene (14.7 g) and a 50/50 wt./wt. % mixture (2.6 g) oftetrafluoroethylene (1.3 g) and carbon dioxide (1.3 g) are condensedinto the reactor at a temperature of below -20° C. and CO₂ (5.2 g) isadded via high pressure syringe pump. The reactor is then slowly heatedto 35.0° C. and held for 3 hours. After the reaction is complete, thecarbon dioxide and excess monomer are vented slowly to the atmosphere,the reactor is opened and the product collected. The product is washedtwice with a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanoland dried under vacuum at elevated temperature. The reaction yields 0.34g of white polymer (26% yield). Thermogravimetric analysis shows a 5%weight loss at 494.0° C. Differential scanning calorimetry shows avirgin melting point of 267.1° C., and a crystallization exotherm at247.9° C. (first cooling).

EXAMPLE 11

TFE/HFP Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Hexafluoropropylene (19.2 g) and a 50/50 wt./wt. % mixture (4.4 g) oftetrafluoroethylene (2.2 g) and carbon dioxide (2.2 g) are condensedinto the reactor at a temperature of below -20° C. and CO₂ (5.1 g) isadded via high pressure syringe pump. The reactor is slowly heated to35.0° C. and held for 4 hours. After the reaction is complete, thecarbon dioxide and excess monomer are vented slowly to the atmosphere,the cell is opened and the product collected. The product is washedtwice with a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanoland dried under vacuum at elevated temperature. The reaction yields 1.8grams of white polymer (72% yield). Thermogravimetric analysis shows a5% weight loss at 447.0° C. Differential scanning calorimetry shows avirgin melting point of 265.8° C., and a crystallization exotherm at248.7° C. (first cooling).

EXAMPLE 12

TFE/HFP

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.03 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Hexafluoropropylene (19.3 g) and a 50/50 wt./wt. % mixture (4.8 g) oftetrafluoroethylene (2.4 g) and carbon dioxide (2.4 g) are condensedinto the reactor at a temperature of below -20° C. and CO₂ (5.1 g) isadded via high pressure syringe pump. The reactor is slowly heated to35.0° C. and held for 4 hours. After the reaction is complete, thecarbon dioxide and excess monomer are vented slowly to the atmosphere,the reactor is opened and the product collected. The product is washedtwice with a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanoland dried under vacuum at elevated temperature. The reaction yields 1.7g of white polymer (71% yield). Thermogravimetric analysis shows a 5%weight loss at 477.0° C. Differential scanning calorimetry shows avirgin melting point of 254.8° C., and a crystallization exotherm at255.3° C. (first cooling). Analysis by FTIR observed 4.3 wt. %hexafluoropropylene incorporation.

EXAMPLE 13

TFE/PMVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.018M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Perfluoro(methyl vinyl ether) (1.4 g) and a 50/50 wt./wt. % mixture(13.1 g) of tetrafluoroethylene (6.6 g) and carbon dioxide (6.6 g) arecondensed into the reactor at a temperature of below -20° C. and CO₂ (10g) is added via high pressure syringe pump. The reactor is slowly heatedto 35.0° C. and held for 3 hours. After the reaction is complete, thecarbon dioxide and excess monomer are vented slowly to the atmosphere,the reactor is opened and the product collected. The product is washedtwice with a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanoland dried under vacuum at elevated temperature. The reaction yields 1.5grams of white polymer (19% yield). Thermogravimetric analysis shows a5% weight loss at 534.7° C. Differential scanning calorimetry shows avirgin melting point at 311.4° C., crystallization exotherm at 278.2° C.(first cooling), and a second order transition at -39° C.

EXAMPLE 14

TFE/PMVE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Perfluoro(methyl vinyl ether) (6.1 g) and a 50/50 wt./wt. % mixture (5.6g) of tetrafluoroethylene (2.8 g) and carbon dioxide (2.8 g) arecondensed into the cell at a temperature of below -20° C. and CO₂ (8 g)is added via high pressure syringe pump. The reactor is slowly heated to35.0° C. and held for 3 hours. After the reaction is complete the CO₂and excess monomer are vented slowly to the atmosphere, the reactoropened, and the product collected. The product is washed twice with a50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol and dried undervacuum at elevated temperature. The reaction yields 2.2 g of whitepolymer (25% yield). Thermogravimetric analysis shows a 5% weight lossat 491.3° C. Differential scanning calorimetry shows the absence of acrystalline melting point.

EXAMPLE 15

PMVE/TFE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Perfluoro(methyl (3.5 g) vinyl ether) (2.5 g) and a 50/50 wt./wt. %mixture (7.0 g) of tetrafluoroethylene (3.5 g) and CO₂ (3.5 g) arecondensed into the reactor at a temperature of below -20° C. and CO₂(11.5) is added via high pressure syringe pump. The reactor is slowlyheated to 35.0° C. and held for 3 hours. After the reaction is completethe CO₂ and excess monomer are vented slowly to the atmosphere, thereactor is opened and the product collected. The product is washed twicewith a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol anddried under vacuum at elevated temperature. The reaction yields 4.9 g ofwhite polymer (80% yield). Thermogravimetric analysis shows a 5% weightloss at 500.7° C. Differential scanning calorimetry shows the absence ofa crystalline melting point.

EXAMPLE 16

VF2/HFP Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.018M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Hexafluoropropylene (15.1 g) and vinylidine fluoride (4.0 g) arecondensed into the reactor at a temperature of below -20° C. and CO₂ (5g) is added via high pressure syringe pump. The reactor is slowly heatedto 35.0° C. and held for 3 hours. After the reaction is complete the CO₂and excess monomer are vented slowly to the atmosphere, the reactor isopened and the product collected. The product is washed twice with a50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol and dried undera vacuum at elevated temperature. The reaction yields 0.27 g of gummytranslucent polymer (7% yield based on vinylidine fluoride).Thermogravimetric analysis shows a 5% weight loss at 456.9° C.Differential scanning calorimetry shows a glass transition at -19.5° C.

EXAMPLE 17

VF2/CTFE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.18M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.020 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Chlorotrifluoroethylene (2.0 g) and vinylidine fluoride (4.5 g) arecondensed into the reactor at a temperature of below -20° C. and CO₂ (10g) is added via high pressure syringe pump. The reactor is slowly heatedto 35.0° C. and held for 3 hours. After the reaction is complete the CO₂and excess monomer are vented slowly to the atmosphere, the reactor isopened and the product collected. The product is washed twice with a50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol and dried undervacuum at elevated temperature. The reaction yields 0.52 g of gummytranslucent polymer (8% yield). Thermogravimetric analysis shows a 5%weight loss at 433.8° C. Differential scanning calorimetry shows glasstransition at -8.3° C.

EXAMPLE 18

VF2/CTFE Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.20 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed.Chlorotrifluoroethylene (3.3 g) and vinylidine fluoride (3.3 g) arecondensed into the reactor at a temperature of below -20° C. and CO₂ (15g) is added via high pressure syringe pump. The reactor is then slowlyheated to 35.0° C. and held for 4 hours. After the reaction is completethe CO₂ and excess monomer are vented slowly to the atmosphere, thereactor is opened and the product collected. The product is washed twicewith a 50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol anddried under vacuum at elevated temperature. The reaction yields 0.71 gof gummy translucent polymer (11% yield). Thermogravimetric analysisshows a 5% weight loss at 427.4° C.

EXAMPLE 19

Vinyl Fluoride Homopolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.015 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed. Vinylfluoride (3.8 g) is condensed into the reactor at a temperature of below-20° C. and CO₂ (15 g) is added via high pressure syringe pump. Thereactor is slowly heated to 35.0° C. and held for 4 hours. After thereaction is complete the CO₂ and excess monomer are vented slowly to theatmosphere, the cell is opened and the product collected. The product iswashed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 0.45 g of gummy translucentpolymer (12% yield). Thermogravimetric analysis shows a 5% weight lossat 407.7° C. Analysis by differential scanning calorimetry showed avirgin melting point of 208.4° C. and a crystallization exotherm at164.7° C. (first cooling).

EXAMPLE 20

TFE/Ethylene Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.015 ml) is added whilemaintaining a positive argon purge, and the reaction is sealed. A 50/50wt./wt. % mixture (8.9 g) of tetrafluoroethylene (4.4 g) and CO₂ (4.4 g)and ethylene (3.4 g) are added to the reactor at a temperature of below-20° C. and CO₂ (10 g) is added via high pressure syringe pump. Thereactor is slowly heated to 35.0° C. and held for 4 hours. After thereaction is complete the CO₂ and excess monomer are vented slowly to theatmosphere, the reactor is opened and the product collected. The productis washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 4.8 grams of white polymer(62% yield). Thermogravimetric analysis shows a 5% weight loss at 458.2°C. Differential scanning calorimetry shows a virgin melting point of231.9° C. and crystallization exotherms at 208.4 and 214.5° C.

EXAMPLE 21

TFE/Ethylene Copolymer

A 25 ml high pressure reactor is chilled to well below 0° C. in a dryice/acetone bath under argon. A 0.24M solution of HFPO dimer peroxideinitiator in 1,1,2-trichlorotrifluoroethane (0.015 ml) is added whilemaintaining a positive argon purge, and the reactor is sealed. A 50/50wt./wt. % mixture (9.3 g) of tetrafluoroethylene (4.6 g) and CO₂ (4.6 g)and ethylene (1.9 g) is added to the reactor at a temperature of below-20° C. and CO₂ (10 g) is added via high pressure syringe pump. Thereactor is slowly heated to 35.0° C. and held for 4 hours. After thereaction is complete the CO₂ and excess monomer are vented slowly to theatmosphere, the reactor is opened and the product collected. The productis washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 2.9 of white polymer (45%yield). Thermogravimetric analysis shows a 5% weight loss at 469.4° C.Differential scanning calorimetry shows virgin melting point of 273.1°C. and a crystallization exotherm at 248.0° C.

EXAMPLE 22

TFE/PPVE Copolymer

A 500 ml high pressure AUTOCLAVE™ fitted with a MAGNADRIVE™ stirrer iscooled to well below 0° C. in a dry ice bath under argon. A 0.24Msolution of bis(perfluoro-2-propoxypropionyl)peroxide in1,1,2-trichlorotrifluoroethane (0.70 ml), methanol (0.10 ml--as a chaintransfer agent), and perfluoro(propyl vinyl ether) (30 ml, 46 g) whichhad previously been sparged with argon, are added while maintaining apositive argon purge and the reactor is sealed. A 50 wt./wt. % mixture(123 g) of tetrafluoroethylene (61.5 g) and carbon dioxide (61.5 g) iscondensed into the reactor at a temperature of below -20° C., and CO₂(190 g) is added via high pressure syringe pump. The reactor is heatedto 35° C. and held for 4 hours at which time heating is discontinued.After the reaction is complete the carbon dioxide and excess monomer arevented to the atmosphere, the reactor is opened, and the productcollected. The product is washed twice with a 50/50 mixture of1,1,2-trichlorotrifluoroethane/methanol and dried under vacuum atelevated temperature. The reaction yields 43 g of product (70% yieldbased on TFE). Thermogravimetric shows a 5% weight loss at 511.5° C.Differential scanning calorimetry shows a virgin melting point of 297.1°C., and a crystallization exotherm at 276.3° C. (first cooling). Endgroup analysis by FTIR found a combined total of 11 acid fluoride andcarboxylic acid end groups per million carbon atoms, in addition to 80methyl ester end groups per million carbon atoms.

EXAMPLE 23

TFE/HFP Copolymer

A 500 ml high pressure AUTOCLAVE™ fitted with a MAGNADRIVE™ stirrer iscooled to well below 0° C. in a dry ice bath under argon. A 0.24Msolution of bis(perfluoro-2-propoxypropionyl)peroxide in1,1,2-trichlorotrifluoroethane (3.0 ml), is added while maintaining apositive argon purge and the reactor is sealed. Hexafluoropropylene (257g) and a 50/50 wt./wt. % mixture (56 g) of tetrafluoroethylene (28 g)and carbon dioxide (28 g) is condensed into the reactor at a temperatureof below -20° C., and CO₂ (100 g) is added via high pressure syringepump. The reactor is heated to 35° C. and held for 4 hours at which timeheating is discontinued. After the reaction is complete the carbondioxide and excess monomer are vented to the atmosphere, the reactor isopened, and the product collected. The product is washed twice with a50/50 mixture of 1,1,2-trichlorotrifluoroethane/methanol and dried undervacuum at elevated temperature. The reaction yields 17.7 g of product(63% yield based on TFE). Thermogravimetric shows a 5% weight loss at471.2° C. Differential scanning calorimetry shows a virgin melting pointof 260.6° C., and a crystallization exotherm at 251.5 ° C. (firstcooling).

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. A polymerization reaction mixture producedby the polymerization of a fluoromonomer in the presence of apolymerization initiator capable of forming stable end groups on afluorinated polymer produced by said polymerization of saidfluoromonomer said reaction mixture comprising:(a) said fluorinatedpolymer having stable end groups, wherein said fluorinated polymer isselected from the group consisting of polymers and copolymers oftetrafluoroethylene, hexafluoropropylene, perfluoromethylvinyl ether,perfluoroethylvinyl ether, perfluoropropylvinyl ether, vinyl fluoride,vinylidene fluoride, chlorotrifluoroethylene, hexafluoroisobutylene, andperfluoro(2,2-dimethyl dioxole); and (b) a polymerization mediumcomprising liquid or supercritical carbon dioxide.
 2. The polymerizationreaction mixture according to claim 1, wherein said polymerizationmedium comprises liquid carbon dioxide.
 3. The polymerization reactionmixture according to claim 1, wherein said polymerization mediumcomprises supercritical carbon dioxide.
 4. The polymerization reactionmixture according to claim 1, further comprising a chain transfer agent.5. The polymerization reaction mixture according to claim 1, whereinsaid polymerization medium further comprises a cosolvent.
 6. Thepolymerization reaction mixture according to claim 1, wherein saidfluorinated polymer is selected from the group consisting of polymers oftetrafluoroethylene, hexafluoropropylene, perfluoromethylvinyl ether,perfluoroethylvinyl ether, perfluoropropylvinyl ether, and vinylidenefluoride.
 7. The polymerization reaction mixture according to claim 1,wherein said fluorinated polymer is selected from the group consistingof copolymers of perfluoropropylvinyl ether and tetrafluoroethylene,copolymers of hexafluoropropylene and tetrafluoroethylene, copolymers ofperfluoromethylvinyl ether and tetrafluoroethylene, copolymers ofvinylidene fluoride and hexafluoropropylene, and copolymers ofvinylidene fluoride and chlorotrifluoroethylene.